JPS5992909A - Preparation of flat plate of polycrystalline silicon - Google Patents

Abstract

PURPOSE:To enable the easy production of a large flat plate of polycrystalline silicon, by forming flat film of molten silicon on a high-melting substrate coated with a low-melting material wettable with molten silicon, and solidifying the molten liquid film. CONSTITUTION:A low-melting material 1.2 (e.g. tin) wettable with molten silicon in liquid state and having poor reactivity is applied to the surface of a high- melting substrate 1.1 (e.g. high purity alumina substrate) in the form of a film of about 200-300mu thick. The raw material silicon 1.3 is heated at 1,450 deg.C in the crucible 1.4 to form molten silicon 2.3. The crucible 1.4 is transferred above the substrate 1.1, the valve 1.5 is opened, and the crucible 1.4 is transferred along the direction of the arrow to form a molten silicon film 2.4 on the surface of the molten film of the low-melting material 2.2. When the temperature of the substrate 1.1 is lowered to about 1,300 deg.C, the molten silicon film 2.4 is solidified to a flat polycrystalling silicon leaving the low-melting material film in liquid state. Accordingly, the polycrystalline silicon plate can be separated easily by using the molten low-melting material film as the lubrication film.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a method for manufacturing a flat silicon crystal.

[Prior art and its problems]

Recently, solar cells have been attracting attention as an energy source.

Conventionally, as a method for manufacturing a flat silicon substrate for a solar cell, there is a method (hereinafter abbreviated as CZ method) in which a cylindrical ingot is grown from a silicon melt. Although this method yields high-quality crystals, it requires a cutting process to process them into flat plates, which results in significant material loss, making the solar cells extremely expensive. Ta.

Furthermore, it has been difficult to obtain a large-area substrate due to technical controls. Therefore, polycrystalline silicon has recently been developed as a low-cost solar cell.

Methods for producing polycrystalline silicon can be broadly classified into three types3.The first technique is a technique for pulling polycrystalline silicon in the form of a υ plate from a silicon melt. This technology includes the EFG method (Edge-def iue 1
-f f 1m (ed-Growtb), Web Law,
ESP (Edgc-8uppoted-pol I
i+ig) method etc. The JIN FG method is a method in which silicon melt is drawn out from a nozzle-shaped molding material and solidified, and attempts to obtain flat polycrystalline silicon by devising the shape and form of the nozzle tip. The polycrystalline substrate is formed as a continuous flat plate extending from the nozzle tip. In the web method, silicon melt is maintained in an appropriately cooled state to grow dendrites, and the silicon melt is shaped into a flat plate by the dendrites. Unlike the web method, the ESP method uses two filaments when molding silicon melt into a flat plate shape. The filament is made of a material that is wettable by the silicon melt. When the filaments are immersed in the melt so as to form the ends in the width direction of the elongated body and pulled up continuously, the silicon melt stretched between the two filaments solidifies, forming a flat plate of polycrystalline silicon. is obtained. The disadvantage of the above three technologies is that the temperature control at the interface where the liquid becomes solid (hereinafter abbreviated as solid-liquid interface) is complicated, and if the temperature control is poor, the continuous growth of flat polycrystalline silicon becomes impossible. . This is because the wider the crystal width, the greater the technical difficulty, making it unsuitable for mass production and unable to provide low-cost flat polycrystalline silicon.

The second technique uses a material that gets wet with the silicon melt.
This is a method of manufacturing polycrystalline silicon by forming a 1111 strong flat plate and converting the silicon melt into a flat V-1 body on the 1111 strong flat plate itself. This technique includes the It, A, D method (R,
i bbonAgainstDrop) method, SCI
M (Si IIcon-Coating-Inver
ted-Meuiscus) method, etc. 1tA1:
The second method is to use carbon as a reinforcing plate, immerse it in a silicon melt, and then pull it out of the liquid to produce a carbon reinforcing plate.Second, polycrystalline silicon is produced. The SCIM method is a method of producing flat polycrystalline silicon by forming a reinforced flat plate with ceramic, adhering carbon powder to the flat surface, and moving it over a funnel-shaped crucible containing silicon melt. be. In the former technique, it is difficult to remove the polycrystalline silicon formed on the carbon reinforced substrate from the reinforced substrate, and the twisting and firing of the carbon reinforced substrate requires a large amount of electric power. In the latter technology, the shape of the ceramic reinforcing flat plate is devised, so there is no need to separate the polycrystalline silicon from the reinforcing flat plate.

The reinforcing plate may become deformed due to heat accumulation, or impurities from the reinforcing plate may stain the grain boundaries of polycrystalline silicon, making it impossible to obtain high-quality polycrystalline silicon. The third technique uses a mold,
This is a method of manufacturing an ingot with a shape according to the mold by directly solidifying the silicon melt in the mold.

Compared to the first and second techniques, this method does not require complicated temperature control and can be easily manufactured.
Similar to the Z method, it is necessary to cut the material into a flat plate to be used as a substrate for a solar cell, and the disadvantage is that there is a large amount of material 11 lost during this process.

[Purpose of the invention]

The present invention was made in consideration of the drawbacks of the above technology, and
The purpose of the present invention is to provide a low-cost solar cell that can easily produce flat polycrystalline silicon and can be mass-produced over a large area.

[Summary of the invention]

The present invention produces flat polycrystalline silicon by creating a flat silicon melt on a high melting point substrate that is wetted with silicon melt and coated with a material with a melting point lower than silicon, and solidifying the silicon melt. This is the way to do it.

〔Effect of the invention〕

The present invention includes a cutting process for obtaining a flat silicon substrate,
The complicated R1 degree control 1 is not required, and a flat silicon substrate can be manufactured easily, and a material with a melting point lower than that of silicon is interposed between the high melting point substrate and the flat silicon substrate. Therefore, it can be easily peeled off, and contamination from the high melting point substrate can be prevented.Furthermore, depending on the high melting point substrate, it is possible to increase the area, so it is effective in providing low-cost solar cells. be.

[Embodiments of the invention]

FIG. 1(a) fb) shows an embodiment of the present invention. 1st
As shown in the figure, a high-purity alumina plate is used as a high-melting point substrate (11), and a low-melting point material (1, 2) of about 200 to 300 microns is adhered onto the substrate. The low melting point material must be a material that can interact with silicon melt in a liquid state and has poor reactivity. The inventors used tin as the low melting point material. The melting point of tin is 23JC, which is sufficiently lower than the melting point of silicon, so it is still in high demand for silicon melt, and
The 4' sign that +W does not form a solid solution is a problem. Said,
¥1 on the top of the alumina board. A crucible (1, 4) for storing raw material silicon (1, 3) is set. Furthermore, a crucible opening/closing mechanism (1, 5) is provided at the tip of the crucible. If there is one misfire, use heating device W (not shown)
was heated to 1450 tr to melt the raw material silicon and tin, forming a silicon melt 71 & (2,3) and a tin melt film (2,2). After that, lower the crucible to just above the one alumina substrate, open the opening/closing mechanism U3, move it in the direction of the arrow in the figure, and apply the silicon melt film (two
, 4> were formed. Furthermore, the inventor has determined that approximately 20C/min
The temperature of the high purity alumina substrate is increased by the heating device at a rate of 13
The temperature was lowered to 00C. Under this temperature condition, the melting point of silicon is 1420t; There is. Therefore, in this state, it is easily possible to remove only the flat polycrystalline silicon using the tin melt film as a lubricating film. Tin attached to flat polycrystalline silicon can be easily removed by applying fL chemical treatment.
ihi de chiru.

The 19th aspect of the present invention is high-purity ju Ni-alumina 7h (plate thickness: N+ie100 m: lX6+li) O(1 mm
When I tested it at JU/min, the soot B'A P+' 5 (10 microns, l!
A polycrystalline silicon having a large crystal grain size was obtained with a thick T5 of x thickness - J of 300 to 500 microns o7.

[Other embodiments of the invention]

2nd and 1 show other examples, (a) ``Tsuji R:l-''
In an actual example device i)'7 for manufacturing flat plate fall/winter crystalline silicon, (b) is the temperature distribution. Place the high-purity alumina substrate on it and move it in the direction of the arrow in the figure to install the movable groove plate (3, 1) 5). In the center of the movable plate, there are a crucible (3, 3>) for storing silicon melt/1g (32) and a heating device (34), and a heat shielding plate (35). The temperature distribution of the moving mechanism plate is maintained at 1450 t; A, (Number of lodging 11
! The upper part is held at 1300C. The present inventors placed a high-purity alumina substrate coated with a tin film of 500 μm thick and measuring 100 mm long x 100 mm wide x 5 mm thick in the area on the left side of FIG. 3. Since the temperature is above the melting point of tin, the tin film on the high-purity alumina substrate undergoes a phase change into a molten liquid. after that,
The silicon melt film is deposited on the upper surface of the tin melt film while being moved to the high temperature region using the movable keyaki structure plate. Since the tin and silicon melt get wet, the silicon melt spreads into the shape of the high-purity alumina substrate.

When the high-purity alumina substrate was further moved by the moving mechanism plate to the area held at 13001r on the right side of Figure 3, the silicon melt on the tin melt film gradually solidified.

All of the silicon melt becomes solid. Therefore.

In the above temperature range, solid high-purity alumina substrate (3,
7), a tin melt film (3, 8), and a flat polycrystalline silicon crystal (3, 9) are formed. While maintaining this situation, take out only the flat polycrystalline silicon using a vacuum chuck (not shown), etc., and then repeat the reverse operation to continuously produce flat polycrystalline silicon. be able to.

As explained above, according to the present invention, a flat silicon melt film is formed on a high-purity, high-melting-point substrate coated with a material that is separate from the silicon melt and has a melting point lower than that of silicon, and is solidified. By doing so, it is possible to easily manufacture a large-area flat polycrystalline silicon. Furthermore, by controlling the temperature distribution and cooling rate of the high-purity alumina substrate to optimal values, it is possible to manufacture tabular polycrystalline silicon with large grain boundaries and improve crystal quality.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the invention, and FIG. 2 is a diagram for explaining another embodiment of the invention. 1.1...High purity alumina substrate. 1.2... Solid tin film, 1.3... Solid raw material silicon, 1.4... Crucible. 1.5... Opening/closing mechanism, 2.2... Tin melt film. 2.3... Melt raw material silicon, 2.4... Silicon melt film.

Claims (3)

[Claims] (1) Production of flat polycrystalline silicon, characterized by forming a flat silicon melt film on a high melting point substrate that is wetted with silicon melt and coated with a material whose melting point is lower than that of silicon, and solidifying it. Method. (2) The method for producing flat polycrystalline silicon according to claim 1, characterized in that tin is used as the material that is wetted by the silicon melt and has a melting point lower than that of silicon. (3) The method for manufacturing flat polycrystalline silicon according to claim 1, characterized in that high-purity alumina is used as the high-melting point substrate.